Synthesis of a crystalline silicoaluminophosphate

ABSTRACT

The present invention is a method for synthesizing non-zeolitic molecular sieves which have a three dimensional microporous framework comprising [AlO 2 ] and [PO 2 ] units. In preparing the reaction mixture, a surfactant is used, coupled with non-aqueous impregnation to prevent acid sites from being destroyed by water during Pt impregnation. The superior SAPO exhibits higher activity and selectivity especially in catalytic hydroisomerization of waxy feeds, due to the presence of medium-sized silica islands distributed throughout the SAPO.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/616,371 application filed Sep. 14, 2012, allowed, which is acontinuation of U.S. patent application Ser. No. 13/252,766, filed Oct.4, 2011, abandoned Sep. 17, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/181,652, filed Jul. 29, 2008, abandoned Oct. 5,2011, the contents of each of which are incorporated herein by referencein their entirety.

FIELD OF THE INVENTION

This invention relates to a new crystalline silicoaluminophosphate(SAPO) molecular sieve and to its synthesis.

BACKGROUND OF THE INVENTION

Silicoaluminophosphates (SAPO) are taught in U.S. Pat. No. 4,440,871,for example. SAPO materials are both microporous and crystalline andhave a three-dimensional crystal framework of PO₂ ⁺, AlO₂ ⁻ and SiO₂tetrahedral units and, exclusive of any alkali metals or other cationwhich may optionally be present, an as-synthesized empirical chemicalcomposition on an anhydrous basis of:

-   -   mR:(Si_(x)Al_(y)R_(z))O₂        wherein “R” represents at least one organic templating agent        present in the intracrystalline pore system; “m” represents the        moles of “R” present per mole of (Si_(x)Al_(y)R_(z))O₂O₂ and has        a value of from 0 to 0.3, the maximum value in each case        depending upon the molecular dimensions of the templating agent        and the available void volume of the pore system of the        particular SAPO species involved; “x”, “y”, and “z” represent        the mole fractions of silicon, aluminum, and phosphorus,        respectively, present as tetrahedral oxides. The minimum value        for each “x”, “y”, and “z” is 0.01 and preferably 0.02. The        maximum value for “x” is 0.98; for “y” is 0.60; and for “z” is        0.52.

Typically, the silicoaluminophosphate molecular sieves are synthesizedby hydrothermally crystallizing a hydrous gel made from substantiallyhomogeneous aqueous reaction mixture containing reactive sources ofaluminum, phosphorus, silicon and the other element(s), if any, requiredin the molecular sieve. The reaction mixture also preferably contains anorganic templating, i.e., structure-directing, agent, preferably acompound of an element of Group VA of the Periodic Table, and/oroptionally an alkali or other metal. The reaction mixture is generallyplaced in a sealed pressure vessel, preferably with an inactive metallicsurface or alternatively, lined with an inert plastic material such aspolytetrafluoroethylene and heated, preferably under autogenouspressure, at a temperature between 50° C. and 250° C., and preferablybetween 100° C. and 200° C., until crystals of the non-zeoliticmolecular sieve product are obtained. Usually this is for a period offrom several hours to several weeks. Effective crystallization timesfrom about 2 hours to about 30 days are generally employed. Themolecular sieve is recovered by any convenient method, for example,centrifugation or filtration.

It is disclosed in U.S. Pat. No. 4,440,871 that while not essential tothe synthesis of SAPO compositions, it has generally been found thatstirring or other moderate agitation of the reaction mixture and/orseeding the reaction mixture with seed crystals of either the SAPOspecies to be produced or a topologically similar aluminophosphate oraluminosilicate composition, facilitates the crystallization procedure.These silicoaluminophosphates exhibit several physical and chemicalproperties which are characteristic of aluminosilicate zeolites andaluminophosphates.

U.S. Pat. No. 4,943,424 describes a SAPO molecular sieve designatedSM-3. It is characterized to distinguish it from all othersilicoaluminophosphate forms as being a silicoaluminophosphate having aphosphorus, silicon, and aluminum concentration at the molecular sievesurface that is different than the phosphorus, silicon, and aluminumconcentration in the bulk of the molecular sieve, and having theessential X-ray diffraction pattern of SAPO-11.

None of the U.S. patents mentioned above discloses or teaches how tomake the crystalline silicoaluminophosphate molecular sieve of thisinvention.

SUMMARY OF THE INVENTION

This invention is a molecular sieve composition having the topology AELand being isostructural with conventional SAPO-11. The composition has aframework of tetrahedrally-arranged silicon, aluminum, and phosphorus.It is designated SM-7, wherein the composition has a ratio of Si atomscoordinated as Si(3AllSi) to that coordinated as Si(4Si) of at least0.5, presence of Si atoms coordinated as Si(4Al) less than 30 mol. % anda mean mesopore diameter of less than 200 angstroms (Å), and morepreferably a ratio of Si atoms coordinated as Si(3AllSi) to thatcoordinated as Si(4Si) of at least 0.8, presence of Si atoms coordinatedas Si(4Al) less than 25 mol. % and a mean mesopore diameter of less than195 angstroms, and most preferably a ratio of Si atoms coordinated as Si(3 AllSi) to that coordinated as Si(4Si) of at least 1, presence of Siatoms coordinated as Si(4Al) less than 23 mol. % and a mean mesoporediameter of less than 190 angstroms (See Table 5). Generally, themolecular sieve compositions of the present invention are intermediatepore molecular sieves (vide infra).

The manufacturing process: A method of manufacturing non-zeoliticmolecular sieve catalyst using a crystalline silicoaluminophosphatemolecular sieve having a three dimensional microporous frameworkstructure of [AlO₂] and [PO₂] units wherein the ratio of Si atomscoordinated as Si(3AllSi) to that coordinated as Si(4Si) of at least0.5, presence of Si atoms coordinated as Si(4Al) less than 30 mol. % andhas a mean mesopore diameter of less than 200 angstroms:

(a) preparing an aqueous reaction mixture containing a reactive sourceof silicon, a reactive source of aluminum, a reactive source ofphosphorus, a surfactant, and an organic templating agent, said reactionmixture having a composition expressed in terms of mole ratios of oxidesof:

-   -   aR:Al₂O₃:nP₂O₅:qSiO₂:bH₂O        wherein R is an organic templating agent; “a” has a value large        enough to constitute an effective amount of R; “b” has a value        such that there are 10 to 40 moles of H₂O per mole of aluminum        oxide (Al₂O₃); said reaction mixture having been formed by        controlling the molar ratio of the templating agent to        phosphorus (as P₂O₅) in the reaction mixture to be greater than        about 0.05 before the molar ratio of aluminum (as Al₂O₃) to        phosphorus (as P₂O₅) in the reaction mixture becomes greater        than about 0.5; heating the reaction mixture at a temperature        and a time sufficient until crystals of silicoaluminophosphate        are formed; combining the crystals of silicoaluminophosphate        with an active source of a hydrogenation component dissolved in        a non-aqueous solvent and removing substantially all of the        non-aqueous solvent at a temperature and for a time sufficient        to produce non-zeolitic silicoaluminophosphate molecular sieve        catalytic particulates; and        (b) recovering the non-zeolitic silicoaluminophosphate molecular        sieve particles.

In step (a), the surfactant is preferably dissolved in alcohol in thesubstantial absence of the silicon source. Following step (c), theparticles may be bound in an extrudate to create a catalyst, prior tometals addition.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 shows the relative activity of SM-7 and SM-3 in lowering the pourpoint of a Fischer-Tropsch wax.

FIG. 2 shows the relative 650° F.+ bottoms yields of SM-7 and SM-3 inlowering the pour point of the Fischer-Tropsch wax used in FIG. 1.

FIG. 3 compares VI of the 650° F.+ bottoms oil made by SM-7 from aFischer-Tropsch wax feedstock with that of the 650° F.+ bottoms oil madewith SM-3.

FIG. 4 shows relative activity of SM-7 catalyst impregnated with Pt inaqueous solution v. impregnated SM-7 in non-aqueous solution andimpregnated SM-3 in non-aqueous solution for lowering the pour point ofthe Fischer-Tropsch wax feedstock used in FIG. 1.

FIG. 5 shows the yield of 650° F.+ bottoms from the Fischer-Tropsch waxused in FIG. 1 was less for the product prepared with the new SM-7catalyst impregnated with Pt in aqueous solution as compared to the newSM-7 catalyst impregnated with Pt in a non aqueous solution and the SM-3catalyst impregnated with Pt in a non aqueous solution.

FIG. 6 shows the viscosity index of the 650° F.+ bottoms oils producedin FIG. 5.

FIG. 7 is a representation of the Si, Al, and P distribution types inSAPO's.

FIG. 8 shows the ²⁹Si-MAS NMR spectrum and Si distribution of a repeatpreparation of SM-3 catalyst.

FIG. 9 shows the ²⁹Si-MAS NMR spectrum and Si distribution of SM-7catalyst.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The molecular sieve catalyst of this invention is useful for thehydroconversion of hydrocarbons. The SM-7 sieve differs from priorintermediate pore silicoaluminophosphate (SAPO) molecular sieves in thefollowing ways: it possesses a smaller mean mesopore diameter, the ratioof Si atoms coordinated as Si(3All Si) to that coordinated as Si(4Si) isat least 0.5, and the presence of Si atoms coordinated as Si(4Al) isless than 30 mol. %. The catalyst utilizing the sieve of this inventionexhibits unique and useful catalytic and shape-selective properties.

The hydroconversion activity of a catalyst is usually determined bycomparing the temperature at which various catalysts must be utilizedunder otherwise constant reaction conditions with the same feedstock andthe same conversion rate of products. The lower the reaction temperaturefor a given extent of reaction, the more active the catalyst is for thespecified process. The silicoaluminophosphate of the present invention,which is a SAPO-11 type silicoaluminophosphate, shows superior activityand selectivity as compared to other known SAPO-11silicoaluminophosphates. The selectivity is a measure of the yield of adesired product.

The silicoaluminophosphate molecular sieve of this invention,as-synthesized, has a crystalline structure whose X-ray powderdiffraction pattern is similar to that of SAPO-11 as disclosed in U.S.Pat. No. 4,440,871. The silicoaluminophosphate molecular sieve assynthesized is characterized as comprising a three-dimensionalmicroporous crystal framework structure of [SiO₂], [AlO₂], and [PO₂]tetrahedral units which has a composition in terms of mole ratio ofoxides on an anhydrous basis expressed by the formula:

-   -   mR:Al₂O₃:nP₂O₅.qSiO₂        wherein “R” represents at least one organic templating agent        referred to as “template” herein present in the intracrystalline        pore system; “m” represents the moles of “R” present and has a        value such that there are from 0.02 to 2 moles of R per mole of        alumina; “n” has a value of from 0.85 to 1.1 and preferably 0.90        to 1, and “q” has a value of from 0.1 to 4 and preferably 0.1        to 1. Generally, the silicoaluminophosphate molecular sieve of        this invention is an intermediate pore (size) molecular sieve        (vide infra).

Alumina is defined in this application as Al₂O₃.

The SM-7 silicoaluminophosphate molecular sieve as synthesized may alsobe expressed in terms of its unit empirical formula. On an anhydrousbasis it is expressed by the formula:

-   -   mR(Si_(x)Al_(y)P_(z))O₂        wherein R and m are defined hereinabove; “x”, “y”, and “z”        represent the mole fraction of silicon, aluminum, and        phosphorus, respectively, present as tetrahedral oxide units.

The SM-7 silicoaluminophosphate is further characterized in that theP₂O₅ to alumina mole ratio at the surface of the silicoaluminophosphateis about 0.80 or less and preferably in the range of 0.80 to 0.55, theP₂O₅ to alumina mole ratio in the bulk of the silicoaluminophosphate is0.85 or greater, preferably in the range of 0.90 to 1.1, and mostpreferably in the range of 0.90 to 1, and the SiO₂ to alumina mole ratioat the surface of the silicoaluminophosphate is greater than the SiO₂ toalumina mole ratio within the bulk of the silicoaluminophosphate.

The silicon content of the sieve is greater at the surface of thesilicoaluminophosphate than in the bulk of the sieve. The term “siliconcontent” at the surface of the sieve refers to the amount of silicon atthe surface of the sample as can be measured using X-ray photoelectronspectroscopy (XPS) surface analysis; this silicon content will includeany amorphous silica that is present. The sieves of this invention havehigher silicon contents at the surface than in the bulk. In thiscomparison, either silica contents per se or the silica/alumina ratioscan be compared.

While often difficult to quantify, the term “porosity,” as used herein,is generally consistent with its IUPAC definition. See Rouquerol et al.,Pure & Appl. Chem., vol. 66, pp. 1739-1758, 1994. To describe acomposition's porosity in terms of pore size, the following terms can beused: “micropore” for pore diameters less than 2 nm, “mesopore” for porediameters in the range of 2-50 nm, and “macropore” for pore diametersgreater than 50 nm. Note that a given material or composition may havepores in two or more such size regimes, e.g., a particle may comprisemacroporosity and microporosity.

By “intermediate pore size,” as used herein and with reference tomolecular sieves (i.e., intermediate pore molecular sieves), is meant aneffective pore aperture in the range of about 5 to 6.5 angstroms (Å)when the molecular sieve is in the H-form. Molecular sieves having poreapertures in this range tend to have unique molecular sievingcharacteristics. Unlike small pore zeolites such as erionite andchabazite, they will allow hydrocarbons having some branching into the:molecular sieve void spaces. Unlike larger pore zeolites such as thefaujasites and mordenites, they can differentiate between n-alkanes andslightly branched alkanes on the one hand and larger branched alkaneshaving, for example, quaternary carbon atoms.

The effective pore size of the molecular sieves can be measured usingstandard adsorption techniques (e.g., BET) and hydrocarbonaceouscompounds of known minimum kinetic diameters. See Breck, ZeoliteMolecular Sieves, 1974 (especially Chapter 8); Anderson et al., J.Catalysis 58, 114 (1979); and Leofanti et al., Catalysis Today 41, 207(1998); all of which are incorporated by reference.

Intermediate pore size molecular sieves in the H-form will typicallyadmit molecules having “kinetic diameters” of 5.0 to 6.5 angstroms withlittle hindrance. Examples of such compounds (and their kineticdiameters in angstroms) are: n-hexane (4.3), 3-methylpentane (5.5),benzene (5.85), and toluene (5.8). Compounds having kinetic diameters ofabout 6 to 6.5 angstroms can be admitted into the pores, depending onthe particular sieve, but do not penetrate as quickly and in some casesare effectively excluded. Compounds having kinetic diameters in therange of 6 to 6.5 angstroms include: cyclohexane (6.0),2,3-dimethylbutane (6.1), 2,2-dimethylbutane (6.2), m-xylene (6.1) and1,2,3,4-tetramethylbenzene (6.4). Generally, compounds having kineticdiameters of greater than about 6.5% do not penetrate the pore aperturesand thus are not absorbed into the interior of the molecular sievelattice. Examples of such larger compounds include: o-xylene (6.8),hexamethylbenzene (7.1), 1,3,5-trimethylbenzene (7.5), and tributylamine(8.1).

The term “unit empirical formula” is used herein according to its commonmeaning to designate the simplest formula which gives the relativenumber of atoms of silicon, aluminum, and phosphorus which form a [PO₂],[AlO₂], and [SiO₂] tetrahedral unit within a silicoaluminophosphatemolecular sieve and which forms the molecular framework of the SM-7composition.

The proportions of the various components in the aqueous reactionmixture affect, inter alia, the rate at which the synthesis progresses,the yield, the crystal framework, the distribution of Si atoms asderived by ²⁹Si MAS NMR, and the porosity of the non-zeolitic molecularsieve.

In the preparation of the aqueous reaction mixture required to preparethe SM-7 molecular sieve, the amounts in which the specific ingredientsare mixed together and the order in which they are mixed together arecritical in forming the specific structure and its physical porosity. Inaccordance with the present invention, a reaction mixture containing areactive source of SiO₂, a source of aluminum such as aluminumisopropoxide, phosphoric acid, and a surfactant, is prepared. Othersources of aluminum that may be used in the preparation of thisnon-zeolitic molecular sieve include aluminum alkoxides other thanaluminum isopropoxide, or a pseudo-boehmite hydrated aluminum oxide.Aluminum isopropoxide is the preferred source of aluminum. U.S. Pat. No.4,310,440, which discloses aluminum phosphate molecular sieves, and U.S.Pat. No. 4,440,871, which discloses silicoaluminophosphates and theirpreparation, list these sources of aluminum for the preparation of thesemolecular sieves. These disclosures are incorporated herein byreference.

The surfactant is preferably a C₈+ alkylamine which may be dissolved inan alcohol or mixture of alcohols. The alcohol is preferably selectedfrom a C₁ to C₈ alcohol or a mixture of such alcohols. The surfactantmay be added without a solvent. The order of addition of reagents to thereaction mixture is adjusted to reduce or eliminate the coagulation ofthe aluminum source in the reaction mixture. Preferably, in preparingthe aqueous reaction mixture, the phosphorus source is added prior tothe addition of the aluminum source. Accordingly, the molar ratio of thetemplating agent to phosphorus (source) in the reaction mixture shouldbe greater than about 0.05, preferably greater than about 0.1, and mostpreferably, greater than about 0.2 before-the ratio of aluminum tophosphorus is greater than about 0.5. Preferably, the above, molarratios of templating agent to phosphorus should be present in thereaction mixture before the molar ratio of aluminum to phosphorus in thereaction is greater than about 0.3, and most preferably greater thanabout 0.25.

The term “templating agent” although used in the singular includes theplural. Thus, if more than one template is used in the reaction mixture,then to determine the molar ratio of the templating agent present in themixture, the molar ratios of each template should be added together.Additionally, the above molar ratio of template includes the amount ofany compound that itself does not contribute to the formation of thedesired molecular sieve but does reduce the viscosity of the reactionmixture. Such a compound would not interfere with the structuredirecting properties of the template. An example would include theaddition of small amines to supplant the extensive use of the highermolecular weight quaternary ammonium compounds.

In preparing a targeted molecular sieve, one of ordinary skill wouldfollow the teachings known in the art for synthesizing the desiredsieve; such as, the amount and types of reagents, crystallizationtemperatures, etc., but, it is critical to the instant invention thatthe molar ratio of the templating agent to phosphorus (source) in thereaction mixture be greater than about 0.05 before the ratio of aluminumto phosphorus in the reaction mixture is greater than about 0.5.Subsequently, in crystallizing the targeted non-zeolitic molecularsieve, the reaction mixture should have the proper molar amounts andproper conditions should be maintained for producing the targetedintermediate pore molecular sieve.

The use and order of addition of the reactants in the reaction mixtureare important in forming the active sieve of this invention. On alaboratory scale where reagents are readily mixed, the crystallizationmethods described in the prior art have been effective in producingmolecular sieves in high yields. However, for larger scale preparationssuch as commercial catalyst manufacture, synthesis techniques requirethe constituents to be combined over a substantially longer period oftime. When the aluminum source is added to the phosphorus source at analuminum to phosphorous atomic ratio of greater than 0.5 without theaddition of template, there is a voluminous coagulum of aluminum specieor species; resulting in a final mixture that is thick, viscous, and notreadily dispersible. Therefore, there is a need for a method forproducing molecular sieves in quantities sufficient for commercialapplications, and that avoids the problematic aluminum coagulation.

As used herein the terms “coagulum” and “precipitate” are usedinterchangeably and refer to the separation and binding together of thereagent, in solid form, in the reaction mix.

As shown in FIG. 7, aluminophosphates or AlPO₄ molecular sieves have aframework of AlO₄ and PO₄ tetrahedra linked by oxygen atoms (not shown).These materials are neutral and do not have any acidity. By replacingsome of the PO₄ tetrahedra by SiO₄, acidity can be introduced to thesematerials, which are known as silicoaluminophosphates or SAPOs. Theoverall acidity of SAPOs depends not only upon the Al content in thesample, but also upon the distribution of the Al in the sample. As shownin FIG. 3, in various scenarios, Si may be surrounded by four Al atomswhen the dispersion is very high or it may be surrounded by four Siatoms when the dispersion is low, forming large Si islands. As shown inFIG. 7, Si atoms also may be surrounded by one, two or three Al atoms.Such Si atoms that are surrounded by one, two or three Al atomsintroduce acidity and are an important characteristic influencingcatalytic activity in SAPO materials.

Since the initial work of Lippmaa et al. (J. Am. Chem. Soc., 102,4889-93, 1980), there have been many studies of the zeolites by ²⁹Simagic angle spinning (MAS) nuclear magnetic resonance (NMR). It wasfirst demonstrated by Lippmaa that the ²⁹Si MAS NMR of zeolites containsfive reasonably well resolved peaks corresponding to the five possibledistributions of Si and Al around a silicon atom of the SiO₄ tetrahedra.The characteristic chemical shift range of the five different localsilicon environments is presented in Table 2.

TABLE 2 Characteristic ²⁹Si MAS NMR Chemical Shift Range of Different SiEnvironment Si Environment Si(4Al) Si(3Al,1Si) Si(2Al,2Si) Si(1Al,3Si)Si(4Si) Chemical Shift −80 to −94 −95 to −99 −100 to −105 −106 to −108−109 to −120- Range (ppm, from Tetra- Methyl Silane)

²⁹Si MAS NMR may be used to estimate the distribution of silicon inSAPOs. However, it must be noted that Si concentrations in SAPOs couldbe as low as 1 wt. % which makes it very difficult to obtain very highquality NMR data. Moreover, these signals are not well resolved as inthe case of zeolites. Consequently, there is some degree of uncertaintyintroduced into deconvolution and in estimating the number of Si atomsin various environments. Nevertheless, the information about theapproximate distribution of Si atoms is high enough to determine theextent of dispersion of silicon in the SAPO materials.

A comparison of ²⁹Si MAS NMR for SM-3 and SM-7 samples is found in theDiscussion of Results section below. The studies revealed that acidicactivity is improved in SM-7, which possesses larger Si islands.

In synthesizing the composition of this invention known as SM-7, it ispreferred that the reaction mixture be essentially free of alkali metalcations, and accordingly a preferred reaction mixture compositionexpressed in terms of mole ratio of oxides is as follows:

-   -   aR:Al₂O₃:nP₂O₅:qSiO₂:bH₂O        wherein “R” is an organic templating agent; “a” has a value        great enough to constitute an effective concentration of “R” and        preferably has a value such that there are from about 0.20 to 2        moles of R per mole of alumina and more preferably about 0.8 to        1.2; “b” has a value such that there is 10 to 60 moles of H₂O        per mole of aluminum oxide, preferably 20 to 50.

In the synthesis method of the present invention, an aqueous reactionmixture is formed by combining the reactive aluminum and phosphorussources, with a portion of the templating agent, in the substantialabsence of the silicon source. The resulting reaction mixture is thencombined with the silicon source and thereafter the mixture is combinedwith the template. If alkali metal cations are present in the reactionmixture, they should be present in sufficiently low concentrations thatthey do not interfere with the formation of the SM-7 composition.

Any inorganic cations and anions which may be present in the reactionmixture are generally not provided by separately-added components.Rather, these cations and anions will frequently come from compoundsadded to the reaction mixture to provide the other essential componentssuch as the silicon source or such as the organic templating agent.

More specifically, the synthesis method comprises:

(a) preparing an aqueous reaction mixture comprising the followingreactants:SiO₂ (silicon source), aluminum isopropoxide (source of aluminum),phosphoric acid (phosphorous source), a surfactant, preferably analcohol, and an organic templating agent, said reaction mixture having acomposition expressed in terms of mole ratios of oxides as:

-   -   aR:Al₂O₃:nP₂O₅:qSiO₂:bH₂O        wherein R is an organic templating agent; “a” has a value large        enough to constitute an effective amount of R; “b” has a value        such that there are 10 to 60 moles of H₂O per mole of aluminum        oxide (Al₂O₃); said reaction mixture having been formed by        combining the reactive aluminum source, reactive phosphorus        source, and the templating agent, wherein a portion of the        templating agent is added prior to complete addition of the        aluminum source and the surfactant (preferably dissolved in        alcohol) in the substantial absence of the silicon-source,        thereafter combining the resulting mixture with the silicon        source to form the complete reaction mixture;        (b) heating the reaction mixture to a temperature in the range        of from 100° C. to 200° C. until crystals of        silicoaluminophosphate are formed; and        (c) recovering said crystals.

The crystallization is conducted under hydrothermal conditions underpressure and usually in an autoclave so that the reaction mixture issubject to autogenous pressure. Following crystallization of the SM-7material, the reaction mixture containing same is filtered and therecovered crystals are washed, for example, with water, and then dried,such as by heating at from at least 25° C. to about 150° C. atatmospheric pressure. Preferably, the supernatant liquid above thecrystals is removed prior to the initial filtering of the crystals.

The SM-7, prepared as depicted in the instant invention, is beneficiallysubjected to thermal treatment to remove the organic templating agent.This thermal treatment is generally performed by heating at atemperature of about 300° C. to about 700° C. for at least 1 minute andgenerally not longer than 20 hours. While sub-atmospheric pressure canbe employed for the thermal treatment, atmospheric pressure is desiredfor reasons of convenience. The thermally treated product isparticularly useful in the catalysis of certain hydrocarbon conversionreactions.

While not intending to be limited to theory, it appears SiO₂ does notenter the structure until late in the crystallization, such that underthe conditions of the process of this invention, in the early phases ofthe reaction, there is produced a near aluminophosphate phase surroundedby a SiO₂-rich amorphous phase. As PO₄ ³ is depleted by reaction withAl⁺³ species, the pH of the mixture rises from about 8-8.5 to about10-10.5. This increases the dissolution of SiO₂ permitting silicaincorporation into the structure such that there is a silica gradientthrough the crystal with more silica near the exterior than at thecenter. The P₂O₅ to alumina (Al₂O₃) mole ratio within the bulk of theSM-7 silicoaluminophosphate is 0.85 or greater, and preferably from 0.90to 1.

The surface silica rich phase on the outside of the sieve contains ahigher SiO₂ to alumina mole ratio than in the bulk. Material with highersurface silica to alumina mole ratios appears to show increased acidityand increased activity.

If necessary, the pH can be lowered into the proper region using acidssuch as HCl or H₃PO₄. The latter may be preferred, since having a slightexcess of PO₄ ³ will help ensure that the PO₄ ³ concentration is neverso low that the alumina and silica components have nothing to react withbut each other.

An excess of water over the described range tends to lead to rapidincorporation of silica into the product. Excess water also leads tolarger crystals which may diminish activity due to diffusionconstraints. In the present invention, a crystallite size of less than 1micron is produced with an average size less than 0.5 micron.

The organic template or directing agent is preferably selected fromdi-n-propylamine and di-isopropylamine or mixtures thereof.

The silica may be any silica source capable of being dissolved and/ordispersed in the liquid reaction mixture. Preferably, the silica isintroduced into the reaction mixture as either a silica sol or as fumedsilica. Useful sources of silicon oxide (silica) include any one or moreforms of silicic acid or silicon dioxide, alkoxy- or other compounds ofsilicon. Preferably, a form of silicon oxide known as CABOSIL (CabotCorp.) is used.

Typically, the crystalline silicoaluminophosphate molecular sieve of theinstant invention has an AEL topology. Other topologies include, but arenot limited to, ATO and AFO. See Atlas of Zeolite Structure Types,Fourth Edition, W. M. Meier, D. H. Olson, and Ch. Baerlocher, Elsevier,1996.

The SM-7 synthesized as described herein can be used as catalyst inintimate combination with a metal component such as silver, tungsten,vanadium, molybdenum, rhenium, chromium, manganese, or a Group VIIImetal, preferably platinum or palladium where, for example, ahydrogenation-dehydrogenation or oxidation function is to be performed.Such a component can be ion-exchanged into the composition, impregnatedtherein, or intimately physically admixed therewith. Such component canbe impregnated into or onto the composition, such as, for example, inthe case of platinum, by treating the crystal with a solution containinga platinum metal-containing ion. Thus, suitable platinum compoundsinclude chloroplatinic acid, platinous chloride, and various compoundscontaining the platinum amine complex. The preferred impregnation of aGroup VIII metal, preferably platinum, is performed in a non-aqueoussolution. Impregnation of metals onto molecular sieves employingnon-aqueous solution is disclosed in U.S. Pat. No. 5,939,349.

Further, the present SM-7, when employed either as an adsorbent,ion-exchanger, or as a catalyst in an organic compound conversionprocess should be dehydrated, at least partially. This can be done byheating to a temperature in the range of about 200° C. to about 600° C.in air or an inert atmosphere, such as nitrogen, etc., and atatmospheric, sub-atmospheric, or super-atmospheric pressures for about30 minutes to about 48 hours. Dehydration can also be performed at roomtemperature merely by placing the crystalline material in a vacuum, buta longer time is required to obtain a sufficient amount of dehydration.Therefore, depending upon the degree of dehydration or thermal treatmentdesired for the SM-7, it may be subjected to heating at a temperature offrom about 200° C. to about 700° C. for a time of from at least 1 minuteto about 48 hours.

The crystals of SM-7 prepared by the instant invention can be used toprepare shaped particles in a variety of sizes. Generally speaking, theparticles can be in the form of a powder, a granule, or a moldedproduct, such as an extrudate having a particle size sufficient to passthrough a 2-mesh (Tyler) screen and be retained on a 400-mesh (Tyler)screen. In cases where the composition is molded, such as by extrusion,the particles can be formed by extrusion before drying, or they can bepartially dried and then extruded.

In the case of many catalysts, it is desired to incorporate the SM-7with another material resistant to the temperatures and other conditionsemployed in organic conversion processes. Such materials include activeand inactive material and synthetic or naturally occurring zeolites aswell as inorganic materials such as clays, silica, alumina, and/or metaloxides. The latter may be either naturally occurring or in the form ofgelatinous precipitates or gels including mixtures of silica and metaloxides. Use of a material in conjunction with the SM-7, i.e., combinedtherewith, which is active, tends to improve the conversion and/orselectivity of the catalyst in certain organic conversion processes.Inactive materials suitably serve as diluents to control the amount ofconversion in a given process so that products can be obtainedeconomically without employing other means for controlling the rate ofreaction. These materials may be incorporated into naturally occurringclays, e.g., bentonite and kaolin, to improve the crush strength of thecatalyst under commercial operating conditions. Said materials, i.e.,clays, oxides, etc., function as binders for the catalyst. It isdesirable to provide a catalyst having very high crush strength becausein commercial use it is desirable to prevent the catalyst from breakingdown into powder-like materials. These clay binders have been employednormally only for the purpose of improving the crush strength of thecatalyst.

Naturally occurring clays which can be composited with the new crystalinclude the montmorillonite and kaolin families which include thesubbentonites, and the kaolins commonly known as Dixie, McNamee,Georgia, and Florida clays or others in which the main mineralconstituent is halloysite, kaolinite, dickite, nacrite, or anauxite.Such clays can be used in the raw state as originally mined or initiallysubjected to calcination, acid treatment, or chemical modification.Binders useful for compositing with the present crystal also includeinorganic oxides, notably alumina or silica.

In addition to the foregoing materials, the catalyst produced can becomposited with a porous matrix material such as aluminum phosphate,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia,and silica-magnesia-zirconia. The relative proportions of finely dividedcrystalline SM-7 material and inorganic oxide gel matrix vary widely,with the crystal content ranging from 1 to 90% by weight and moreusually, particularly when the composite is prepared in the form ofbeads, in the range from about 2 to about 80 weight percent of thecomposite.

The crystalline material produced by the present process is readilyconvertible to catalytically active material for a variety of organic,e.g., hydrocarbon compound conversion processes.

SM-7 catalyst, when containing a hydrogenation promoter, can be used ina process for selectively producing middle distillate hydrocarbons byhydrocracking a hydrocarbonaceous feed wherein at least 90% of the feedhas a boiling point above about 600° F. The hydrocracking conditionsinclude reaction temperatures which generally exceed about 500° F. (260°C.) and are usually above about 600° F. (316° C.), preferably betweenabout 600° F. (316° C.) and about 900° F. (482° C.). Hydrogen additionrates should be at least about 400, and are usually between about 1,000and about 15,000 standard cubic feet per barrel. Reaction pressuresgenerally exceed 200 psig (13.7 bar), and are usually within the rangeof about 500 to about 3000 psig (32.4 to 207 bar). Liquid hourly spacevelocities are less than about 15, preferably between about 0.2 andabout 10.

The conditions should be chosen so that the overall conversion rate willcorrespond to the production of at least about 40%, and preferably atleast about 500% of products boiling below about 725° F. (385° C.) perpass and preferably below about 725° F. and above about 300° F.Midbarrel selectivity should be such that at least about 40%, preferablyat least about 50%, of the product is in the middle distillate range andpreferably below about 725° F. and above about 300° F. The process canmaintain conversion levels in excess of about 50% per pass atselectivities in excess of 60% to middle distillate products boilingbetween about 300° F. (149° C.) and about 725° F. (385° C.). The pourpoint of the middle distillate effluent obtained by the process will bebelow about 0° F., and preferably below −20° F.

The process can be operated as a single-stage hydroprocessing zone. Itcan also be the second stage of a two-stage hydrocracking scheme inwhich the first stage removes nitrogen and sulfur from the feedstockbefore contact with the middle distillate-producing catalyst. Thecatalyst can also be used in the first stage of a multi-stephydrocracking scheme. In operation as the first stage, the middledistillate-producing zone also denitrifies and desulfurizes thefeedstock; in addition, it allows the second stage using the samecatalyst or a conventional hydrocracking catalyst to operate moreefficiently so that, overall, more middle distillates are produced thanin other process configurations.

In the process of the invention, the hydrocarbon feedstock is heatedwith the catalyst under conversion conditions which are appropriate forhydrocracking. During the conversion, aromatics and naphthenes which arepresent in the feedstock undergo hydrocracking reactions such asdealkylation, ring opening, and cracking, followed by hydrogenation.Long-chain paraffins, which are also present in the feedstock, undergomild cracking reactions to yield non-waxy products of higher molecularweight than compared to products obtained using the prior art dewaxingzeolitic catalysts such as ZSM-5, and at the same time, a measure ofisomerization takes place so that not only is the pour point reduced byreason of the cracking reactions described above, but in addition then-paraffins become isomerized to isoparaffins to form liquid-rangematerials which contribute to low viscosity, lower pour point products.

The feedstock for the process of the invention comprises a heavyhydrocarbon oil such as a gas oil, coker tower bottoms fractions,reduced crude, vacuum tower bottoms, deasphalted vacuum resids, FCCtower bottoms, cycle oils, Fischer Tropsch waxy feeds, waste polymers orbiomass (including vegetable oils and other triglycerides). Oils derivedfrom coal, shale, or tar sands may also be treated in this way. Oils ofthis kind generally boil above 600° F. (316° C.) although the process isalso useful with oils which have initial boiling points as low as 436°F. (260° C.). Preferably at least 90% of the feed will boil above atleast 600° F. (316° C.) and most preferably at least about 90% of thefeed will boil between about 700° F. (371° C.) and about 1200° F. (649°C.). These heavy oils comprise high molecular weight long-chainparaffins and high molecular weight ring compounds with a largeproportion of fused ring compounds. During the processing, both thefused ring aromatics and naphthenes and paraffinic compounds are crackedby the SM-7 containing catalyst to middle distillate range products. Asubstantial fraction of the paraffinic components of the initialfeedstock also undergo conversion to isoparaffin.

The process is of particular utility with highly paraffinic feedsbecause, with feeds of this kind, the greatest improvement in pour pointmay be obtained. However, most feeds will contain a certain content ofpolycyclic compounds.

The process enables heavy feedstocks, such as gas oils, boiling above600° F. to be more selectively converted to middle distillate rangeproducts having improved pour points in contrast to prior processesusing large pore catalysts, such as zeolite Y.

The hydrocracking catalysts contain an effective amount of at least onehydrogenation catalyst (component) of the type commonly employed inhydrocracking catalysts. The hydrogenation component is generallyselected from the group of hydrogenation catalysts consisting of one ormore metals of Group VIB and Group VIII, including the salts, complexes,and solutions containing such. The hydrogenation catalyst is preferablyselected from the group of metals, salts, and complexes thereof of thegroup consisting of at least one of platinum, palladium, rhodium,iridium, and mixtures thereof or the group consisting of at least one ofnickel, molybdenum, cobalt, tungsten, titanium, chromium, and mixturesthereof. Reference to the catalytically active metal or metals isintended to encompass such metal or metals in the elemental state or insome form such as an oxide, sulfide, halide, carboxylate, and the like.

The hydrogenation catalyst is present in an effective amount to providethe hydrogenation function of the hydrocracking catalyst, and preferablyin the range of from 0.05 to 25% by weight.

The SM-7 may be employed in conjunction with traditional hydrocrackingcatalysts, e.g., any aluminosilicate heretofore employed as a componentin hydrocracking catalysts. Representative of the zeoliticaluminosilicates disclosed heretofore as employable as component partsof hydrocracking catalysts are Zeolite Y (including steam stabilized,e.g., ultra-stable Y), Zeolite X, Zeolite beta (U.S. Pat. No.3,308,069), Zeolite ZK-20 (U.S. Pat. No. 3,445,727), Zeolite ZSM-3 (U.S.Pat. No. 3,415,736), faujasite, LZ-10 (U.K. Patent No. 2,014,970, Jun.9, 1982), ZSM-5-type zeolites, e.g., ZSM-5, ZSM-11, ZSM-12, ZSM-23,ZSM-35, ZSM-38, ZSM-48, crystalline silicates such as silicalite (U.S.Pat. No. 4,061,724), erionite, mordenite, offretite, chabazite,FU-1-type zeolite, NU-type zeolites, LZ-210-type zeolite, and mixturesthereof. Traditional cracking catalysts containing amounts of Na₂O lessthan about 1% by weight are generally preferred. The relative amounts ofthe SM-7 component and traditional hydrocracking component, if any, willdepend, at least in part, on the selected hydrocarbon feedstock and onthe desired product distribution to be obtained therefrom, but in allinstances an effective amount of SM-7 is employed. When a traditionalhydrocracking catalyst (THC) component is employed, the relative weightratio of the THC to the SM-7 is generally between about 1:10 and about500:1, desirably between about 1:10 and about 200:1, preferably betweenabout 1:2 and about 50:1, and most preferably is between about 1:1 andabout 20:1.

The hydrocracking catalysts are typically employed with an inorganicoxide matrix component which may be any of the inorganic oxide matrixcomponents which have been employed heretofore in the formulation ofhydrocracking catalysts including: amorphous catalytic inorganic oxides,e.g., catalytically-active silica-aluminas, clays, silicas, aluminas,silica-aluminas, silica-zirconias, silica-magnesias, alumina-borias,alumina-titanias and the like, and mixtures thereof. The traditionalhydrocracking catalyst and SM-7 may be mixed separately with the matrixcomponent and then mixed or the THC component and SM-7 may be mixed andthen formed with the matrix component.

SM-7 can be used in a process to dewax hydrocarbonaceous feeds (inaddition to lube oils, these would include waxy middle distillates,including those derived from petroleum, Fischer-Tropsch, and vegetableoil feedstocks). The catalytic dewaxing conditions are dependent inlarge measure on the feed used and upon the desired pour point.Generally, the temperature will be between about 200° C. and about 475°C., preferably between about 250° C. and about 450° C. The pressure istypically between about 15 psig and about 3000 psig, preferably betweenabout 200 psig and 3000 psig. The liquid hourly space velocity (LHSV)preferably will be from 0.1 to 20, preferably between about 0.2 andabout 10.

Hydrogen is preferably present in the reaction zone during the catalyticdewaxing process. The hydrogen to feed ratio is typically between about500 and about 30,000 SCF/bbl (standard cubic feet per barrel),preferably about 1000 to about 20,000 SCF/bbl. Generally, hydrogen willbe separated from the product and recycled to the reaction zone.

It has been found that the present process provides selective conversionof waxy n-paraffins to non-waxy paraffins. During processing, the waxyparaffins undergo mild cracking reactions to yield non-waxy products ofhigher molecular weight than compared to products obtained using theprior art zeolitic catalyst. At the same time, a measure ofisomerization takes place, so that not only is the pour point reduced byreason of the cracking reactions described above, but the n-paraffinsadditionally become isomerized to isoparaffins to form liquid rangematerials that contribute to a low viscosity, low pour point product.

The present process may be used to dewax a variety of feedstocks rangingfrom relatively light distillate fractions up to high boiling stockssuch as whole crude petroleum, reduced crudes, vacuum tower residua,cycle oils, synthetic crudes (e.g., shale oils, tar sand oils, etc.),gas oils, vacuum gas oils, FT waxy streams, vegetable and othertriglyceride oils, foot oils, and other heavy oils. The feedstock willnormally be a C₁₀+ feedstock generally boiling above about 350° F. sincelighter oils will usually be free of significant quantities of waxycomponents. However, the process is particularly useful with waxydistillate stocks such as middle distillate stocks including gas oils,kerosenes, and jet fuels, lubricating oil stocks, heating oils and otherdistillation fractions whose pour point and viscosity need to bemaintained within certain specification limits. Lubricating oil stockswill generally boil above 230° C. (450° F.), more usually above 315° C.(600° F.). Hydroprocessed stocks which include stocks which have beenhydrotreated to lower metals, nitrogen, oxygen, and sulfur levels and/orhydrocracked, are a convenient source of stocks of this kind and also ofother distillate fractions since they normally contain significantamounts of waxy n-paraffins. The feedstock of the present process willnormally be a C₁₀+ feedstock containing paraffins, olefins, naphthenes,aromatics, and heterocyclic compounds and with a substantial proportionof higher molecular weight n-paraffins and slightly branched paraffinswhich contribute to the waxy nature of the feedstock. During theprocessing, the n-paraffins and the slightly branched paraffins undergosome cracking or hydrocracking to form liquid range materials whichcontribute to a low viscosity product. The degree of cracking whichoccurs is, however, limited so that the gas yield is reduced, therebypreserving the economic value of the feedstock.

Typical feedstocks include light gas oils, heavy gas oils, and reducedcrudes boiling above 350° F.

While the process herein can be practiced with utility when the feedcontains organic nitrogen (nitrogen-containing impurities), it ispreferred that the organic nitrogen content of the feed be less than 50wppm, more preferably less than 10 wppm.

When used in some embodiments of the present process, the SM-7 isemployed in admixture with at least one Group VIII metal as, forexample, the noble metals such as platinum and palladium, and optionallyother catalytically active metals such as molybdenum, vanadium, zinc,etc. The amount of metal ranges from about 0.01% to 10% and preferably0.2 to 5% by weight of the molecular sieve.

The Group VIII metal utilized in the process of this invention can meanone or more of the metals in its elemental state or in some form such asthe sulfide or oxide and mixtures thereof. As is customary in the art ofcatalysis, when referring to the active metal or metals, it is intendedto encompass the existence of such metal in the elementary state or insome form such as the oxide or sulfide as mentioned above, andregardless of the state in which the metallic component actually exists,the concentrations are computed as if they existed in the elementalstate.

The SM-7 silicoaluminophosphate molecular sieve can be composited withother materials resistant to the temperatures and other conditionsemployed in the dewaxing process. Such matrix materials include activeand inactive materials and synthetic or naturally occurring zeolites aswell as inorganic materials such as clays, silica, alumina, and metaloxides. Examples of zeolites include synthetic and natural faujasites(e.g., X and Y), erionites, mordenites, and those of the ZSM series,e.g., ZSM-5, etc. The combination of zeolites can also be composited ina porous inorganic matrix.

SM-7 can be used in a process to prepare lubricating oils. The processcomprises (a) hydrocracking in a hydrocracking zone a hydrocarbonaceousfeedstock to obtain an effluent comprising a hydrocracked oil; and (b)catalytically dewaxing in a catalytic dewaxing zone the hydrocracked oilof step (a) with a catalyst comprising a crystallinesilicoaluminophosphate SM-7 and a Group VIII metal, preferably platinumor palladium.

Another embodiment of this process includes an additional step ofstabilizing said dewaxed hydrocrackate by catalytic hydrofinishing.

The hydrocarbonaceous feeds from which lube oils are made usuallycontain aromatic compounds as well as normal and branched paraffins ofvery long chain lengths. These feeds usually boil in the gas oil range.Preferred feedstocks are vacuum gas oils with normal boiling ranges inthe range of 350° C. to 600° C., and deasphalted residual oils havingnormal boiling ranges from about 480° C. to about 650° C. Reduced toppedcrude oils, shale oils, liquified coal, coke distillates, flask orthermally cracked oils, atmospheric residua, and other heavy oils canalso be used. The first step in the processing scheme is hydrocracking.In commercial operations, hydrocracking can take place as a single-stepprocess, or as a multi-step process using initial denitrification ordesulfurization steps, all of which are well known.

The present process may be used to upgrade a variety of feedstocksranging from relatively light distillate fractions such as kerosene andjet fuel up to high boiling stocks such as whole crude petroleum,reduced crudes, vacuum tower residua, cycle oils, synthetic crudes(e.g., shale oils, tars and oil, etc.), gas oils, vacuum gas oils, footsoils, and other heavy oils. Straight chain n-paraffins either alone orwith only slightly branched chain paraffins having 16 or more carbonatoms are sometimes referred to herein as waxes. The feedstock willoften be a C₁₀+ feedstock generally boiling above about 350° F. sincelighter oils will usually be free of significant quantities of waxycomponents. However, the process is particularly useful with waxydistillate stocks such as middle distillate stocks including gas oils,kerosenes, and jet fuels, lubricating oil stocks, heating oils and otherdistillate fractions whose pour point and viscosity need to bemaintained within certain specification limits. Lubricating oil stockswill generally boil above 230° C. (450° F.), more usually above 315° C.(600° F.). Hydroprocessed stocks are a convenient source of stocks ofthis kind and also of other distillate fractions since they normallycontain significant amounts of waxy n-paraffins. The feedstock of thepresent process will normally be a C₁₀+ feedstock containing paraffins,olefins, naphthenes, aromatic and heterocyclic compounds and with asubstantial proportion of higher molecular weight n-paraffins andslightly branched paraffins which contribute to the waxy nature of thefeedstock. During the processing, the n-paraffins and the slightlybranched paraffins undergo some cracking or hydrocracking to form liquidrange materials which contribute to a low viscosity product. The degreeof cracking which occurs is, however, limited so that the yield ofproducts having boiling points below that of the feedstock is reduced,thereby preserving the economic value of the feedstock.

Typical feedstocks include light gas oils, heavy gas oils and reducedcrudes boiling above 350° F. Such feedstocks generally have an initialpour point above about 0° C., more usually above about 20° C. Theresultant products after the process is completed generally have pourpoints which fall below −0° C., more preferably below about −10° C.

As used herein, the term “waxy feed” includes petroleum waxes. Thefeedstock employed in the process of the invention can be a waxy feedwhich contains greater than about 50% wax, even greater than about 90%wax. Highly paraffinic feeds having high pour points, generally aboveabout 0° C., more usually above about 10° C. are also suitable for usein the process of the invention. Such a feeds can contain greater thanabout 70% paraffinic carbon, even greater than about 90% paraffiniccarbon.

Exemplary additional suitable feeds for use in the process of theinvention include waxy distillate stocks such as gas oils, lubricatingoil stocks, synthetic oils such as those by Fischer-Tropsch synthesis,high pour point polyalphaolefins, foots oils, synthetic waxes such asnormal alphaolefin waxes, slack waxes, de-oiled waxes andmicrocrystalline waxes. Foots oil is prepared by separating oil from thewax. The isolated oil is referred to as foots oil.

The feedstock may be a C₂ 0+ feedstock generally boiling above about600° F. The process of the invention is useful with waxy distillatestocks such as gas oils, lubricating oil stocks, heating oils and otherdistillate fractions whose pour point and viscosity need to bemaintained within certain specification limits. Lubricating oil stockswill generally boil above 230° C. (450° F.), more usually above 315° C.(600° F.). Hydroprocessed stocks are a convenient source of stocks ofthis kind and also of other distillate fractions since they normallycontain significant amounts of waxy n-paraffins. The feedstock of thepresent process may be a C₂ 0+ feedstock containing paraffins, olefins,naphthenes, aromatics and heterocyclic compounds and a substantialproportion of higher molecular weight n-paraffins and slightly branchedparaffins which contribute to the waxy nature of the feedstock. Duringprocessing, the n-paraffins and the slightly branched paraffins undergosome cracking or hydrocracking to form liquid range materials whichcontribute to a low viscosity product. The degree of cracking whichoccurs is, however, limited so that the yield of low boiling products isreduced, thereby preserving the economic value of the feedstock.

Slack wax can be obtained from either a hydrocracked lube oil or asolvent refined lube oil. Hydrocracking is preferred because thatprocess can also reduce the nitrogen content to low values. With slackwax derived from solvent refined oils, deoiling can be used to reducethe nitrogen content. Optionally, hydrotreating of the slack wax can becarried out to lower the nitrogen content thereof. Slack waxes possess avery high viscosity index, normally in the range of from 140 to 200,depending on the oil content and the starting material from which thewax has been prepared. Slack waxes are therefore eminently suitable forthe preparation of lubricating oils having very high viscosity indices,i.e., from about 120 to about 180.

Feeds also suitable for use in the process of the invention arepartially dewaxed oils wherein dewaxing to an intermediate pour pointhas been carried out by a process other than that claimed herein, forexample, conventional catalytic dewaxing processes and solvent dewaxingprocesses. Exemplary suitable solvent dewaxing processes are set forthin U.S. Pat. No. 4,547,287.

Typically, hydrocracking process conditions include temperatures in therange of about 250° C. to about 500° C., pressures in the range of about425 to 3000 psig, or more, a hydrogen recycle rate of 400 to 15,000SCF/bbl, and a LHSV (v/v/hr) of 0.1 to 50.

Hydrogenation-dehydrogenation components of the hydrocracking catalystusually comprise metals selected from Group VIII and Group VIB of thePeriodic Table, and compounds including them. Preferred Group VIIIcomponents include cobalt, nickel, platinum, and palladium, particularlythe oxides and sulfides of cobalt and nickel. Preferred Group VIBcomponents are the oxides and sulfides of molybdenum and tungsten. Thus,examples of hydrocracking catalysts which are preferred for use in thehydrocracking step are the combinations nickel-tungsten-silica-aluminaand nickel-molybdenum-silica-alumina.

A particularly preferred hydrocracking catalyst for use in the presentprocess is nickel sulfide/tungsten sulfide on a silica-alumina basewhich contains discrete metal phosphate particles (described in U.S.Pat. No. 3,493,517, incorporated herein by reference).

The nitrogen content of the hydrocrackate is as low as is consistentwith economical refinery operations, but is: preferably less than 50 ppm(w/w), and more preferably less than about 10 ppm (w/w), and mostpreferably less than about 1 ppm (w/w).

The hydrocracking step yields two significant benefits. First, bylowering the nitrogen content, it dramatically increases the efficiencyand ease of the catalytic dewaxing step. Second, the viscosity index(VI) is greatly increased as the aromatic compounds present in the feed,especially the polycyclic aromatics, are opened and hydrogenated. In thehydrocracking step, increases of at least 10 VI units will occur in thelube oil fraction, i.e., that fraction boiling above 230° C. and morepreferably above 315° C.

The hydrocrackate is preferably distilled by conventional means toremove those products boiling below 230° C., and more preferably below315° C. to yield one or more lube oil boiling range streams. Dependingupon the particular lube oil desired, for example, a light, medium, orheavy lube oil, the raw hydrocrackate may be distilled into light,medium, or heavy oil fractions. Among the lower boiling products removedare light nitrogen containing compounds such as NH₃. This yields a lubeoil stream with a reduced nitrogen level, so that the SM-7 crystallinesilicoaluminophosphate molecular sieve in the dewaxing catalyst achievesmaximum activity in the dewaxing step. Lubricating oils of differentboiling ranges can be prepared by the process of this invention. Thesewould include light neutral, medium neutral, heavy natural, and brightstock, where the neutral oils are prepared from distillate fractions andbright stock from residual fractions.

The great efficiency of the present invention comes in part from thecombination of hydrocracking to produce a very low nitrogen, highviscosity index stock which is then extremely efficiently dewaxed toachieve a very low pour point and improved viscosity and viscosityindex. It can be appreciated that the higher the activity of thedewaxing catalyst, the lower the reactor temperature necessary toachieve a particular degree of dewaxing. A significant benefit is,therefore, the greater energy savings from using the enhanced efficiencycatalyst and usually longer cycle life. Additionally, since the SM-7crystalline silicoaluminophosphate dewaxing catalyst is shape-selective,it reacts preferentially with the waxy components of the feedstockresponsible for high pour points, i.e., the normal paraffins as well asthe slightly branched paraffins and alkyl-substituted cycloparaffinswhich comprise the so-called microcrystalline wax.

When used in the present process, the SM-7 silicoaluminophosphate ispreferably employed in admixture with at least one of the noble metalsplatinum, palladium, and optionally other catalytically active metalssuch as molybdenum, nickel, vanadium, cobalt, tungsten, zinc, etc., andmixtures thereof. The amount of metal ranges from about 0.01% to 10% andpreferably 0.2 to 5% by weight of the molecular sieve.

The metal utilized in the process of this invention can mean one or moreof the metals in its elemental state or in some form such as the sulfideor oxide and mixtures thereof. As is customary in the art of catalysis,when referring to the active metal or metals it is intended to encompassthe existence of such metal in the elementary state or in some form suchas the oxide or sulfide as mentioned above, and regardless of the statein which the metallic component actually exists the concentrations arecomputed as if they existed in the elemental state.

The dewaxing step may be carried out in the same reactor as thehydrocracking step but is preferably carried out in a separate reactor.The catalytic dewaxing conditions are dependent in large measure on thefeed used and upon the desired pour point. Generally, the temperaturewill be between about 200° C. and about 475° C., preferably betweenabout 250° C. and about 450° C. The pressure is typically between about15 psig and about 3000 psig, preferably between about 200 psig and 3000psig. The liquid hourly, space velocity (LHSV) will generally be from0.1 to 20, and preferably between about 0.2 and about 10.

Hydrogen is preferably present in the reaction zone during the catalyticdewaxing process. The hydrogen to feed ratio is typically between about500 and about 30,000 SCF/bbl (standard cubic feet per barrel),preferably about 1,000 to about 20,000 SCF/bbl. Generally, hydrogen willbe separated from the product and recycled to the reaction zone.

The SM-7 crystalline silicoaluminophosphate molecular sieve can becomposited with other materials resistant to the temperatures and otherconditions employed in the dewaxing process. Such matrix materialsinclude active and inactive materials and synthetic or naturallyoccurring zeolites as well as inorganic materials such as clays, silica,alumina, and metal oxides. Examples of zeolites include synthetic andnatural faujasites (e.g., X and Y), erionites, mordenites, and those ofthe ZSM series, e.g., ZSM-5, etc. The combination of zeolites can alsobe composited in a porous inorganic matrix.

It is often desirable to use mild hydrogenation (sometimes referred toas hydrofinishing) to produce more stable lubricating oils.

The hydrofinishing step can be performed either before or after thedewaxing step, and preferably after. Hydrofinishing is typicallyconducted at temperatures ranging from about 190° C. to about 340° C. atpressures from about 400 psig to about 3000 psig at space velocities(LHSV) between about 0.1 and 20 and hydrogen recycle rates of 400 toabout 1500 SCF/bbl. The hydrogenation catalyst employed must be activeenough not only to hydrogenate the olefins, diolefins, and color bodieswithin the lube oil fractions, but also to reduce the aromatic content.The hydrofinishing step is beneficial in preparing an acceptably stablelubricating oil since lubricant oils prepared from hydrocracked stockstend to be unstable to air and light and tend to form sludgesspontaneously and quickly.

Suitable hydrogenation catalysts include conventional metallichydrogenation catalysts, particularly the Group VIII metals such ascobalt, nickel, palladium, and platinum. The metal is typicallyassociated with carriers such as bauxite, alumina, silica gel,silica-alumina composites, and crystalline aluminosilicate zeolites.Palladium is a particularly preferred hydrogenation metal. If desired,non-noble Group VIII metals can be used with molybdates. Metal oxides orsulfides can be used. Suitable catalysts are detailed, for instance, inU.S. Pat. Nos. 3,852,207; 4,157,294; 3,904,153; and 4,673,487, all ofwhich are incorporated herein by reference.

The improved process of this invention will now be illustrated byexamples which are not to be construed as limiting the invention asdescribed in this specification including the attached claims.

EXAMPLES Comparative Example 1A

502 Grams of 86% H₃PO₄ were placed in a stainless steel beaker in an icebath. To this were added 240 grams of ice with mixing. 308 grams ofaluminum isopropoxide (Al[OC₃H₇]₃) plus 841 grams of ice were then addedslowly with mixing using a Polytron. Then 98 grams of di-n-propylaminewere added slowly with mixing, followed by another 571 grams of aluminumisopropoxide and 250 grams of ice. Next, an additional 98 grams ofdi-n-propylamine were slowly added with continued mixing. Then 64 gramsof fumed silica (CABOSIL M-5) were added with mixing. The mixture had apH of 9.2 and the following composition, expressed in molar ratios ofoxides:

-   -   0.90 di-n-propylamine: 0.45 SiO₂: Al₂O₃: 0.98 P₂O₅: 36 H₂O

The mixture was placed in a stainless steel liner in a 1-gallon stirredautoclave and heated for two days at 190° C. and autogenous pressure.The product was filtered, washed with water, dried overnight in a vacuumoven at 120° C., and calcined in air for 8 hours at 593° C. Total weight(volatiles free) of calcined sieve recovered was 426 grams.

The calcined product was analyzed by x-ray diffraction. The product wasfound to be SAPO-11 type (AEL).

The molecular sieve was impregnated with 0.4 wt % Pt, dried, andcalcined according to U.S. Pat. No. 5,939,349.

Example 1

The sieve synthesis of the above example was repeated, but this time 85grams of hexadecylamine dissolved in 300 grams of 1-pentanol were addedprior to the addition of silica. As in the above example, the product byx-ray diffraction analysis was found to be SAPO-11 type (AEL).

The molecular sieve was impregnated with 0.4 wt % Pt by non-aqueousimpregnation according to U.S. Pat. No. 5,939,349, dried, and calcinedas in the above example.

Comparative Example 2A

The catalyst of Comparative Example 1A was tested in a high-pressurepilot plant for isomerization of a hydrotreated Fischer-Tropsch wax(Table I).

TABLE I Inspections of Hydrotreated FT Wax Gravity, API 41.2 Sim. Dist.,LV %, F. ST/5 445/567 10/30 621/710 50 787 70/90 868/970 95/EP 1009/1095

Run conditions were 0.85 LHSV, 300 psig total pressure, and 5 MSCF/bblonce-through hydrogen. The liquid product went directly to a stripperwhich cut that product at 650° F. Reactor temperature was adjusted togive a pour point in the 650° F.+ stripper bottoms of −28° C.

Example 2

The catalyst of Example 1 was tested with the hydrotreatedFischer-Tropsch wax of Table I at the same conditions as in ComparativeExample 2A. FIG. 1 shows this catalyst (labeled “SM-7”) to besubstantially more active than the catalyst of Comparative Example 1A(labeled “SM-3”), due to lower range of operating temperatures.

The yield of 650° F.+ bottoms was also greater for the product preparedwith the catalyst of Example 1 (see FIG. 2).

At the same time, the viscosity index of the 650° F.+ oil was the sameas with the 650° F.+ oil made with the catalyst of Comparative Example1A (see FIG. 3).

Example 3

A sample of the sieve of Example 1 was again impregnated with 0.4 wt %Pt, but this time using an aqueous solution of platinumtetraaminedinitrate. It was then dried and calcined as in Example 1.

Example 4

The catalyst of Example 3 was tested with the hydrotreatedFischer-Tropsch wax of Table I at the same conditions as in ComparativeExample 2A. FIG. 4 shows this catalyst of Example 3 (labeled “SM-7, Aq”)to be substantially less active than the catalyst of Example 1 (labeledSM-7″), and less active than the catalyst of Comparative Example 1A(labeled “SM-3”).

The yield of 650° F.+ bottoms was also much less for the productprepared with the catalyst of Example 3 (see FIG. 5).

The viscosity index of the 650° F.+ oil was about the same as with the650° F.+ oil made with the catalyst of Comparative Example 1A (see FIG.6).

Example 5

The catalyst of Example 1 was analyzed for bulk composition by aninductively-coupled plasma (ICP) technique, and for surface compositionby X-ray photoelectron spectroscopy (XPS) surface analysis, as taught inU.S. Pat. No. 4,943,424, herein incorporated by reference. Bulk analysisshowed 20.2 wt % P, 19.1 wt % Al and 4.53 wt % Si. P/Al atom ratio was0.92, Si/P atom ratio was 0.25, and Si/Al atom ratio was 0.23. ESCAshowed P/Al atom ratio of 0.77, Si/P atom ratio of 1.01, and Si/Al atomratio of 0.78.

Discussion of Results of Comparative Studies of ²⁹Si MAS NMR for SM-3and SM-7 SAPO′S

SM-7 molecular sieve was compared to the composition of a well knownprior art molecular sieve referred to as SM-3. Both catalysts showedsimilar X-ray diffraction patterns and had similar chemicalcompositions; however they differed in pore size distribution and Sidistribution. SM-7 shows superior activity as compared to the well knownSM-3 or prior art.

Standard pore size distribution analysis was performed using nitrogen(adsorption) on the SM-7 silicoaluminophosphate sieve, a SM-3silicoaluminophosphate (Synthesis A), and a repeat SM-3silicoaluminophosphate preparation (Synthesis B), where both Synthesis Aand Synthesis B were similar to the synthesis in Comparative Example 1A.The results shown in Table 5 reveal that the SM-7 sieve had asignificantly greater geometric mesopore surface area, and asignificantly smaller mean mesopore diameter, compared to the SynthesisA SM-3 and Synthesis B SM-3 sieve.

TABLE 5 Mean mesopore Geometric diameter Geometric mesopore Sample(angstroms) mesopore surface diameter SM-7 179.49 ang. 71.54 m²/g  75.74ang. SM-3 Synthesis A 233.23 ang. 49.92 m²/g 131.05 ang. Prep. SM-3Synthesis B 217.51 ang. 49.89 m²/g 103.91 ang. Prep.

U.S. Pat. No. 6,303,534 teaches using ²⁹Si MAS NMR as a method indistinguishing the composition of SAPO molecular sieves when thechemical composition analysis and X-Ray Diffraction analysis aresimilar. This analysis method is routinely used to determine thedistribution of silicon in SAPO molecular sieves. As shown in FIG. 9,aluminophosphates or AlPO₄ molecular sieves have a framework of AlO₄ andPO₄ tetrahedra linked by oxygen atoms (not shown). These materials areneutral and do not have any acidity. By replacing some of the PO₄tetrahedra by SiO₄, acidity can be introduced to these materials, whichare called silicoaluminophosphates or SAPOs. The overall acidity ofSAPOs depends not only upon the Si content in the sample but alsodistribution of the Si in the sample. The Si may be surrounded by fourAl atoms when the dispersion is very high or it may be surrounded byfour Si atoms when the dispersion is poor forming large Si islands.Table 2 shows the characteristic chemical shift range of the fivedifferent local silicon environments. Si atoms may also be surrounded byone, two, or three Al atoms which induce acidity and are important forinfluencing the catalytic activity in SAPO materials.

The ²⁹Si MAS NMR studies of the SAPO samples were carried out withproton decoupling and were recorded on a Bruker Avance 500 Spectrometermade by Bruker BioSpin Corporation located in Billerica, Ma. Thespectrometer was equipped with a 4 mm MAS probe with resonance frequencyof 99.35 MHz for ²⁹Si MAS NMR. Typical experimental conditions were:2000 to 8000 acquisitions; 4 to 5 microsecond pulse width; 60 to 120seconds relaxation delay. All chemical shifts were reported in ppm andmeasured relative to tetramethyl silane (TMS). The deconvolutions of theNMR spectra were carried out using gNMR software version 5.0 marketed byIvorySoft. The spectra were deconvoluted into five silicon environments.Table 2 shows the characteristic chemical shift range of the differentsilicon environments in ppm from a TMS standard.

Results from the ²⁹Si MAS NMR analysis of SM-3 and SM-7 sievepreparations are shown in FIGS. 8 and 9. Each figure shows a ²⁹Si MASNMR (bottom trace) and a simulated spectrum (top trace).

In FIG. 8 the Synthesis B sample of the SM-3 sieve is shown with its²⁹Si MAS NMR spectra and simulated spectra. The Si is distributed infour of the Si environments, the Si(4Al), Si(3Al,1 Si), the Si(2Al,2Si),and the Si(1Al,3Si). The deconvolution ²⁹Si MAS NMR data associated withFIG. 8 (see Table 3) confirms this Si distribution and indicates veryhigh dispersion of the Si without forming the Si islands.

TABLE 3 Distribution of Si in SAPO 11 determined as pictured in FIG. 7(first four rows) and that determined from the simulation of ²⁹Si MASNMR spectrum of SM-3 (FIG. 8) and SM-7 (FIG. 9). 29Si MAS NMR (%) % SiSi Island Ratio Distribution of Si 4Al0Si 3Al1Si 2Al2Si 1Al3Si 0Al4SiDispersed %3Al1Si %0Al4Si Si(3Al1Si)/Si(4Si) High Dispersion 100 0 0 0 0100 — — — Small Islands 0 60 8 20 12 0 60 12 5.0 Medium Islands 0 40 228 30 0 40 30 1.3 Large Islands 0 22 0 11 67 0 22 67 0.3 SM-3 36.5 19.522.5 21.5 0 36.5 19.5 0.0 — SM-7 13.8 22.9 21.4 25.8 16.1 13.8 27 18.51.5

In FIG. 9, the SM-7 sieve is shown with its ²⁹Si MAS NMR spectra andsimulated spectra. The Si is distributed in all five of the Sienvironments, the Si(4Al), Si(3Al,1 Si), the Si(2Al,2Si), theSi(1Al,3Si), and the Si(0Al,4Si). The deconvolution ²⁹Si MAS NMR data(see Table 3) associated with FIG. 9 confirms this Si distribution andindicates lower dispersion of the Si than in SM-3 due to the formationof the Si islands where Si atoms are surrounded by four Si atoms(Si(0Al,4Si)). If Si dispersion in the catalyst is considered as theonly criteria influencing the catalyst activity, one skilled in the artwould expect poorer catalytic activity for molecular sieve sample SM-7.However, when the activity of this new sieve was measured it showedsuperior activity as compared to the SM-3 sieve preparations of theprior art.

SM-7 is found to have a greater density of medium-sized silica islandsthan SM-3. Such islands have a ratio of Si atoms coordinated asSi(3AllSi) to that coordinated as Si(4Si) of 0.5 to 3.5, preferably fromabout 1 to about 3 and most preferably from 1 to 2. The greater densityof medium-sized silica islands confers superior catalytic activity forwax isomerization, at least in part due to the greater proportion ofSi(1Al3Si) sites associated with these islands, as seen in Table 3. Asseen from that table, SM-7 contains 25.8% of the Si in Si(1Al3Si), asopposed to only 21.5% for SM-3. It is believed that these sites areassociated with the strong acid functionality necessary for waxisomerization. Table 4 illustrates the improved dewaxing resultsobtained using Pt/SM-7 catalyst as compared with Pt/SM-3 catalyst.Catalyst A of Table 4 is a Pt/SM-7 catalyst made using the sieve ofExample 1, and Catalyst B is a Pt/SM-3 catalyst made using a sievesimilar to that of Comparative Example 1A. Catalyst A shows a lowerBrookfield viscosity at −40° C.

TABLE 4 Comparative Data-Dewaxed Fischer-Tropsch Base Oils PP Run/HourCatalyst A B Kinematic Viscosity @ 100° C., cSt 2.548 4.146 7.261 4.194Kinematic Viscosity @ 40° C., cSt 8.788 10.19 17.57 39.23 17.53Viscosity Index 123 143 151 149 Cold Crank Viscosity @ −35° C., cP 1,622Cold Crank Viscosity @ −30° C., cP 904 Pour Point, ° C. −20 −14 CloudPoint, ° C. −12 −11 RWI 0.18 0.43 WNF −0.36 −0.62 API Gravity 41.8Molecular Weight (D2502) 412 Molecular Weight (VPO) Brookfield Viscosity@ −40° C., 3440 8,810 cP, 0.2% treat Brookfield Viscosity @ −40° C.,3,530 5,300 cP, 0.4% treat Noack, wt. % (calculated) 14.94 TGA Noack,wt. % 15.96 SIMDIST TBP (WT %), F. TBP @0.5 652 657 TBP @5 694 699 TBP@10 715 719 TBP @20 746 746 TBP @30 770 769 TBP @40 791 791 TBP @50 811813 TBP @60 831 835 TBP @70 851 860 TBP @80 875 885 TBP @90 907 916 TBP@95 936 940 TBP @99.5 1025 998 SIMDIST TBP (LV %), F. TBP @0.5 651 656TBP @5 692 697 TBP @10 713 716 TBP @20 743 744 TBP @30 767 767 TBP @40788 788 TBP @50 809 810 TBP @60 828 832 TBP @70 849 857 TBP @80 872 882TBP @90 904 913 TBP @95 933 938 TBP @99.5 1022 996 Catalyst A is aPt/SM-7 catalyst made using the sieve of Example 1, and Catalyst B is aPt/SM-3 catalyst made using a sieve similar to that of ComparativeExample 1A.

The catalyst also possesses a ratio of Si atoms coordinated asSi(3AllSi) to that coordinated as Si(4Si) of at least 0.5, with thepresence of Si atoms coordinated as Si(4Al) less than 40 mol. %.Preferably, the catalyst possesses a ratio of Si atoms coordinated asSi(3AllSi) to that coordinated as Si(4Si) of at least 0.8, with thepresence of Si atoms coordinated as Si(4Al) less than 30 mol. %. Mostpreferably, the catalyst possesses a ratio of Si atoms coordinated asSi(3AllSi) to that coordinated as Si(4Si) of at least 1.0, with thepresence of Si atoms coordinated as Si(4Al) less than 25 mol. %.

That which is claimed is:
 1. A process for preparing asilicoaluminophosphate molecular sieve, comprising: (a) preparing anaqueous reaction mixture containing a reactive source of silicon, areactive source of aluminum, a reactive source of phosphorus, asurfactant and an organic templating agent; and (b) heating the reactionmixture at a temperature and a time sufficient until crystals of thesilicoaluminophosphate molecular sieve are formed; wherein the reactionmixture is formed by controlling the molar ratio of the templating agentto phosphorus source in the reaction mixture to be greater than about0.05 before the molar ratio of aluminum source to phosphorus source inthe reaction mixture becomes greater than about 0.5.
 2. The process ofclaim 1, wherein the molar ratio of templating agent to phosphorus isgreater than about 0.1 before the aluminum to phosphorus molar ratioreaches about 0.5.
 3. The process of claim 1, wherein the molar ratio oftemplating agent to phosphorus source is greater than about 0.2 beforethe aluminum source to phosphorus source molar ratio reaches about 0.5.4. The process of claim 1, wherein the molecular sieve comprises a meanmesopore diameter of less than 200 angstroms.
 5. The process of claim 1,wherein the silicoaluminophosphate molecular sieve has the ²⁹Si MAS NMRspectrum of FIG.
 9. 6. The process of claim 1, wherein thesilicoaluminophosphate molecular sieve has a three dimensionalmicroporous framework structure of [AlO₂] and [PO₂] units wherein theratio of Si atoms coordinated as Si(3AllSi) to that coordinated asSi(4Si), as determined by ²⁹Si MAS NMR, is at least 0.5, the presence ofSi atoms coordinated as Si(4Al) is less than 40 mol. %.
 7. The processof claim 1, wherein the silicoaluminophosphate molecular sieve isselected from the group consisting of AEL, ATO and AFO.
 8. The processof claim 1, wherein the silicoaluminophosphate molecular sieve is AEL.9. The process of claim 1, aqueous reaction mixture is formed by: (a)combining the surfactant, reactive aluminum and phosphorus sources, witha portion of the templating agent, in the substantial absence of thesilicon source; (b) adding the silicon source; and (c) adding theremaining portion of the templating agent.
 10. The process of claim 9,wherein in step (a), the surfactant is dissolved in alcohol in thesubstantial absence of the silicon source.
 11. The process of claim 1,wherein in step (a), the surfactant is dissolved in alcohol in thesubstantial absence of the silicon source.
 12. The process of claim 1,wherein the aqueous reaction mixture additionally comprises an alcohol.13. The process of claim 12, wherein the alcohol is selected from thegroup consisting of C₁-C₈ alcohols.
 14. The process of claim 12, whereinthe alcohol is 1-pentanol.
 15. The process of claim 1, wherein theorganic templating agent is selected from the group consisting ofdi-n-propylamine, diisopropylamine, and mixtures thereof.
 16. Theprocess of claim 1, wherein the surfactant is selected from C₈₊alkylamines.
 17. The process of claim 16, wherein the surfactant ishexadecylamine.
 18. A process for preparing a silicoaluminophosphatemolecular sieve, comprising: (a) preparing an aqueous reaction mixturecontaining a reactive source of silicon, a reactive source of aluminum,a reactive source of phosphorus, a surfactant and an organic templatingagent, wherein the reaction mixture is prepared by: (i) combining thesurfactant, reactive aluminum and phosphorus sources, with a portion ofthe templating agent, in the substantial absence of the silicon source,(ii) adding the silicon source, and (iii) adding the remaining portionof the templating agent; and (b) heating the reaction mixture at atemperature and a time sufficient until crystals of thesilicoaluminophosphate molecular sieve are formed; wherein the reactionmixture is formed by controlling the molar ratio of the templating agentto phosphorus source in the reaction mixture to be greater than about0.05 before the molar ratio of aluminum source to phosphorus source inthe reaction mixture becomes greater than about 0.5.
 19. The process ofclaim 18, wherein the silicoaluminophosphate molecular sieve has the²⁹Si MAS NMR spectrum of FIG.
 9. 20. The process of claim 18, whereinthe silicoaluminophosphate molecular sieve has a three dimensionalmicroporous framework structure of [AlO₂] and [PO₂] units wherein theratio of Si atoms coordinated as Si(3AllSi) to that coordinated asSi(4Si), as determined by ²⁹Si MAS NMR, is at least 0.5, the presence ofSi atoms coordinated as Si(4Al) is less than 40 mol. %.
 21. The processof claim 18, wherein the silicoaluminophosphate molecular sieve isselected from the group consisting of AEL, ATO and AFO.
 22. The processof claim 18, wherein the silicoaluminophosphate molecular sieve is AEL.